1. Field of the Invention
This invention relates to a shot arranging method that avoids the need for special chips used in semiconductor printing apparatus, and particularly relates to a divisional printing apparatus (stepper) using reduction projection exposure.
2. Description of the Prior Art
Generally, semiconductor printing apparatus are such that a pattern provided on a mask which is a negative is printed onto a wafer, and as the method of printing such pattern onto the wafer, there is a type in which the printing is effected in a single shot (collective printing) and a type in which the printing is effected in a plurality of shots (divisional printing). The collective printing is used in cases where the printing is effected with the mask and the wafer brought into contact with each other (the contact method); in cases where the printing is effected with the mask and the wafer opposed to each other with a minute gap therebetween and without an intermediary imaging system (the proximity method) and in cases where the printing is effected with the mask and the wafer separated sufficiently from each other and with the mask and the wafer maintained in an imaging relationship by a one-to-one magnification imaging system using a lens system or a mirror system (the one-to-one magnification projection method). That is, in the collective printing method, the pattern of the mask is printed intact onto the wafer at one time. In the collective printing method, however, a difficulty in making the mask has been encountered particularly when an element dense in its degree of integration is to be formed, because the desired pattern to be printed onto the wafer is minute and the pattern provided on the mask also is of the same one-to-one magnification shape as the pattern of the wafer.
With this point taken into account, the pattern of the mask has been reduced and projected onto the wafer by the use of a lens system the imaging magnification of which is smaller than 1 and such pattern has been printed onto the wafer. The mask and the wafer are moved relative to each other at each shot so that the exposed areas thereof do not overlap each other, and the same pattern is printed as that in case of the collective printing onto the effective area of the wafer by a plurality of shots.
If divisional printing by such reduction projection exposure is carried out, the pattern provided on the mask is made larger than the pattern to be printed onto the wafer by an inverse number times of the imaging magnification of the imaging system and thus, the difficulty with which the mask is manufactured is reduced. Where divisional printing is carried out, there is a method in which a stage is moved rectilinearly at each shot as shown in FIG. 1 of the accompanying drawings. In this method, the stage is moved rectilinearly, for example, in the X direction so that the errors in the X direction and the Y direction do not accumulate with respect to the feed accuracy of the stage.
In FIG. 1, letter a designates a wafer, letter b denotes the areas to be exposed at each shot, numbers indicate the order of shots, and arrows indicate the feed direction.
As regards the shots, 4 to 5 and 28 to 29 are shown as oblique movement, but these are concerned with the non-effective areas and, as regards effective areas only, rectilinear movement takes place.
This method, however, has the following disadvantages.
In the case of the so-called multichip shot in which a plurality of chips are exposed at one time at each shot, there are many unusable chips which are not printed onto the wafer. This is a problem which arises particularly when divisional printing is mingled with the collective printing. Such problem occurs because, during divisional printing, an effort is made so that the alignment key pattern for collective printing and special chip areas such as test chips are not exposed.
That is, in FIG. 1, shot arrangement is effected so that special chip areas c are not exposed during the divisional printing. However, since there is no shot which includes a special chip area, no chip is printed onto the portion in this shot area except the special chip area and in case of a "1-shot 4-chip" multichip shot, three unusable chips d are produced.
The above-noted problem also holds true of the so-called die-by-die alignment in which alignment is effected at each shot.